Saturn's rings show surprising features

Friday, 2 July 2004 Ben Berkowitz and Gina KeatingReuters

Cassini's view of a gap in Saturn's rings known as the Encke gap. The image was taken after successful entry into Saturn's orbit and shows the sunlit side of the rings (Image: NASA/JPL/Space Science Institute)

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The Cassini spacecraft has sent its first images of Saturn's majestic rings back to Earth, showing surprisingly sharp edges and ripples of energy within the mysterious formations.

Scientists also got a bonus from the early data, the sounds of Saturn, as the craft passed through the "bow shock", or leading edge of the planet's magnetic field, which ebbs and flows like the ocean.

The noise had a deep quality, rising to a guttural crescendo at the point where Cassini met the field.

Though they had little time to analyse what they were seeing and hearing, scientists said the data could help them explain the birth of the entire solar system.

"If you want to understand how the solar system was formed, you go to Saturn," said Dr Carolyn Porco, leader of the Cassini imaging science team.

Program manager Dr Robert Mitchell said the craft was in perfect health after a seven-year journey and had entered orbit so precisely that team leaders were now debating whether they needed to make a corrective move planned for the weekend.

Crisp edges surprise scientists

The early photos, taken from the unlit side of the rings, were black and white and full of electronic "noise", but were clear enough to show fine ring structures and edges that were unexpectedly sharp, given all the colliding particles.

"Ring scientists love sharp edges. They're very mysterious; they have to be held sharp by some mechanism," Porco said.

A second set of images, taken from the sunlit side of the rings, arrived about two hours later and was far sharper, showing the rings and gaps in much greater detail. With illumination, the close-up view of the "A" set of rings made them look something like the surface of a vinyl record.

Scientists were thrilled with the quantity and clarity of the images, the closest pictures of the rings that will be taken during the mission, in some cases five times sharper than those taken by the Voyager missions more than 20 years ago.

The images showed "density waves", disruptions in the particles in the rings caused by the energy of moonlets passing outside them, which scientists said could best be compared to the pattern of bunching and thinning out seen in traffic jams.

They also showed "bending waves", where the rings had been warped by the effects of the passing moons.

Scientists also constructed their first full image of the planet's magnetosphere, using a new instrument flying for the first time on Cassini. The Voyager probes had been able to capture only part of the magnetic bubble that surrounds the planet.

Mission scientists, many of whom have devoted more than a decade to the Cassini project, cheered and called the photos "beautiful" and "mind-blowing".

"Even though we have had a long time to think about our images, we planned them, we chose the exposures, the filters, we know what we were looking at," Porco said from the NASA Jet Propulsion Laboratory in California.

"I am surprised at how surprised I am at the beauty and the clarity of these images.

"They are shocking to me," she said. "Some images were so shocking I thought my team here was playing tricks on me and showing me a simulation of the rings and not the rings itself."

New phase of mission

The truck-sized probe slipped through those rings and entered orbit around Saturn on Thursday, Australian time, after traveling 2.2 billion miles since its October 1997 launch.

Along the way, it used the gravity of Venus, Earth and Jupiter to slingshot it out to the sixth planet from the sun.

Cassini is set to spend at least four years studying the planet, its rings and some of its 31 known moons.

It carries on its back a smaller craft, Huygens, which is designed to break away in December and plummet onto the surface of Saturn's largest moon Titan for a brief study of its atmosphere.

Huygens will touch down on Titan 20 days later, making it the first man-made object to land on another planet's moon.